Manufacture of ammonium sulphate



Jan. 19, 1937. BRAGG 2,067,899

MANUFACTURE OF. AMMONIUM SULPHATE Filed Jan. 20, 1932 1N VEN T OR.

BY I I 4 Q A YDZORZRYK actress UNETED STATES. PATENT OEFIQE 2,067,899MANUFACTURE or AMMONIUM SULPHATE This invention rela ammonium sulphate.

Gilbert A. Bra

Pittsburgh, 3a., assignor, by

mesne assignments, to Koppcrs Company, a corporation of DelawareApplication January 1 claim.

tes to the manufacture of An object of the present invention is toprovide a process by which ammonium sulphate may be efllciently andeconomically manufactured on a commercial scale,

and a further object is to provide a process which is particularlyuseful in gas manufacturing plants for the recovery of byproductswithout any considerable additional equipment.

The process of the present invention comprises contactingammonia-containing gases, such as ammonia still gases, introducingsulphur with an aqueous medium and dioxide and oxygen or air to produceammonium sulphate.

The aqueous medium is preferably maintained at a temperature which willbring about a rapid reaction to form a high yield of ammonium sulphateand also to prevent contamination by substances present in the ammoniastill gases.

maintaining the aqueous medium in acid condition, which is readily ingan excess of accomplished by introducsulphur dioxide, substantially noneof the hydrogen sulphide which may be present in still gases passthrough.

" By maintaining the heated condition and hydrogen sulphide is will beabsorbed but will aqueous medium both in a in an acid condition, the

more likely to pass through than when the aqueous medium is atrelatively low temperatures or when it is'in' neutral or alkalinecondition, monium sulphate these conditions with although the formationof amwill take'place under any of relatively different results.

By maintaining the solution above, for example,

100 C the steam in the not condense in'the aqueous porization isavoided.

The present process ammonia still gaseswill medium and revais preferablycarried on in such a manner that substantially no dilution of theaqueous medium occurs.

'The ammonia still gases contain moisture'which is Carried into theaqueous" medium, and" in sweeping the oxygenf containing gasesthroughthe aqueous medium, the

carry out moisture.

r gases leaving the surface of the aqueous medium Conditions may becontrolled so that the moisture carried out in substantially equal tothe by the volume of the moisture carried in, whereaqueous medium ismaintained substantially constant.

If desired, condition dilution of the aqueous medium may to take placeby conde in by the still gases.

s may be so controlled that be permitted nsation of moisture carriedDilution may be accom- 20, 1932, Serial No. 587,630

(o1, ga -r19) plished by maintaining the temperature somewhat below thatrequired to maintain the volume ofthe aqueous medium constant. e

For instance, assuming that the ammonia still gases contain, underordinary operating conditions, about one pound of ammonia to nine poundsof water vapor, and assuming that the oxidizing gases introduced containabout 8% sulphur dioxide, the temperature of the aqueous medium must bekept at approximately 93 to 94 C.'inorder to maintain the volumeconstant. To bring about dilution, the temperature of the aqueous mediummay be kept below 93 to 94 C., and to bring about concentration thetemperature may be kept above 93 to 94 C. for any desired period.

In the accompanying drawing showing for purposes of exemplification apreferred. formand manner in which'the invention may be embodied andpracticed, the, single figure is an elevational view, partially in crosssection, of apparatus employed in connection with the present process ina preferred arrangement.

The apparatus shown in the accompanying drawing comprises an ammoniastill i of well known construction and a chamber 2 in whichammoniumsulphate is produced. The ammonia still I is of the typeordinarily employed in distilling ammonia liquor'obtained in thescrubbing of gases particularly coal gases produced in' coaldistillation plants and comprises a free ammonia section 3, a lime leg 4and a fixed ammonia section 5.

Steam is introduced into the bottom of the lime leg 4 through a pipe 6provided with a valve 1 and into the bottom of the fixed ammonia section5 through a pipe 8providedwith a valve 9. The still is charged through apipe it which conducts the ammonia liquor into the 'top of the freeammonia section 3 and the still waste is withdrawn from the bottomthrough a pipe'll. The free ammonia section 3 is provided with adephlegmator l2 and'a pipe l3 which conducts the vapors from thedephlegmator into the chamber 2.

The chamber 2 which may be of any desired height is provided with aporous plate M which is supported above the bottom of the chamber. Thepipe i3 is directed into the chamber and terminates a relatively shortdistance above the plate I4. The end of the pipe I3 is preferablyprovided with a distributor l5.

A pipe it provided with a valve I! enters the chamber below the plate l4and is employed for introducing sulphur dioxide and oxygen. An outletpipe It? provided with a valve I9 is connected to the top of the chamber2.

The chamber 2 may be provided with a heating jacket 25 to which areconnected pipes 2| and 22 provided with valves 23 and 24, respectively,for circulation of a heating fluid, or a cooling medium.

A pipe 25 provided with a valve 26 enters the chamber 2 above the plateM for charging the chamber with the aqueous medium to be used in theprocess. An overflow pipe 21 provided with a valve 28 is connected tothe chamber 2 above the plate I 4 and leads to a trough 29.

A pipe 30 provided with a valve Si is connected to the trough 29 andleads to a crystallizer or cooler 32. A branch pipe 33 provided with avalve 34 is connected to the pipe 39 for withdrawing the aqueous mediumfrom the system.

Beneath the crystallizer 32 is a centrifuge 35 to which is connected apipe 36 for withdrawing mother liquor. The pipe 36 leads to a pump 3!which pumps the mother liquor through a pipe 38 provided with a valve 39to the chamber 2 above the plate 14.

In carrying out the process of the present in-- vention in the apparatusdescribed, an aqueous medium such as plain water or preferably asolution containing ammonium sulphate is charged into the chamber 2through the pipe 25. For most purposes the solution introduced ispreferably a saturatedsolution of ammonium sulphate, as for instance asolution containing around 550 grams of ammonium sulphate per literat 20C. When commencing the process with water, this condition may beeventually arrived at while proceeding with the process.

The still I is operated in the usual manner and the vapors therefrom areintroduced into and distributed in the aqueous medium in the chamber 2while at the same time sulphur dioxide and air or gases containing freeoxygen are introduced into the chamber 2 through the pipe l6 beneath theplate I 4. The sulphur dioxide may be obtained for instance byburningsulphur or sulphide ores or hydrogen sulphide gas. It is mixed with airor oxygen in any desired proportions. Satisfactory results are obtainedfrom mixtures of 5 to 8% by volume of sulphur dioxide in air.

The operation of the still and the introduction of the sulphur dioxideand oxidizing gases are controlled so that the aqueous medium ispreferably in an acid condition and so that the ammonia is substantiallyentirely absorbed thereby.

The sulphur dioxide and air are introduced into the solution in a finelycomminuted state by means of the porous plate I4. Any well known andsuitable comminuting means may be employed.

To maintain a high efficiency, the aqueous medium in the chamber 2 ispreferably heated to a temperature of from substantially 80 C. to theboiling point of the solution formed. By the proper manipulation ofvalves IT, IS, 28 and the still I, the treatment in the chamber 2 may becarried on above atmospheric pressures. Pressures as well astemperatures may be varied in order to bring about condensation orevaporation of Water vapor.

Waste gases are withdrawn through the pipe l8 and when the ammonialiquor contains sulphides these waste gases will contain hydrogensulphide which may be removed by any well known means. If the ammonialiquor treated in the still I is substantially free from sulphurcompounds the vapors in the pipe it will be substantially free fromhydrogen sulphide.

The solution formed in the chamber 2 may be withdrawn continuously orintermittently through thepipe 21 and passed into the crystallizer 32.By cooling the solution below the point at which a saturated ammoniumsulphate solution is obtained, crystals of ammonium sulphate willseparate out and the resulting slurry may be centrifuged in thecentrifuge 35. The mother liquor is pumped back to the chamber 2 throughthe pipe 38.

Under certain conditions described in an application of Fred Denig,Serial No. 586,322, filed January 13, 1932, conditions may be socontrolled in the chamber 2 that ammonium bisulphate is formed, in whichcase this may be withdrawn through the pipe 33 to produce therefrom thenormal sulphate by a further treatment with ammonia, as described in theaforesaid application.

It is found that in producing ammonium sulphate in the manner described,proportionately high yields of relatively pure ammonium sulphate areobtained at a relatively low cost. One of the principal items of cost inthe production of ammonium sulphate is in the evaporation of Water toobtain crystallization of ammonium sulphate. By the present process thenecessity for evaporation to obtain crystallization. is practicallyeliminated.

The invention as hereinbefore set forth is embodied in a particular formbut may be variously embodied within the scope of the claim hereinaftermade.

I claim as my invention:

In a process of preparing ammonium sulphate directly from 802, ammoniaand oxygen which bath to thereby form ammonia sulphate'directly from theS02, oxygen and ammonia in the bath, the improvement comprising:introducing the ammonia as ammonia still gases resulting fromdistillation and maintaining the temperature of the bath atapproximately 93 to 94 C. in order to maintain the volume constant andwithdrawing the spent ammonia still gases from the bath while stillcontaining their original content of water vapor.

GILBERT A. BRAGG.

